The present invention relates to an accumulator that is available for storage of pressurized liquid, shock absorption or the like.
In a bladder type accumulator, an inner space of a container main body is partitioned by a bladder into a gas chamber and a liquid chamber, and liquid is made to flow into or from the liquid chamber as opposed to a gas pressure in the gas chamber.
However, if a liquid pressure in the liquid chamber should exceed an allowable limit, or if the gas pressure should be lowered due to leakage of the gas in the gas chamber, then liquid exceeding a predetermined volume would enter the container main body, hence the bladder would be contracted exceeding an allowable compression range, and eventually the bladder would be pushed into a gas feed port of the gas chamber or the like and would be damaged.
Therefore, in order to prevent such accidents, bladder type accumulators associated with a sensor as referred to in the following have been employed. For instance, a bladder type accumulator associated with the so-called shutter type sensor, in which a holder projecting into a bladder and both leg end portions of a U-shaped optical fiber accommodated in the holder are fixedly secured to a top, wall plate of a container main body, a shutter is provided in the midway of the optical fiber, and a driver for that shutter is disposed one set on the outer periphery of the holder as disclosed in Japanese Utility Model Application No. 60-192945 (1985), and a bladder type accumulator associated with the so-called umbrella type sensor, in which a holder projecting into a bladder is provided on a top wall plate of a container main body, a lower limit sensor of umbrella shape is provided at the bottom end portion of the holder, and an upper limit sensor of umbrella shape is provided above the lower limit sensor as disclosed in Japanese Utility Model Application No. 60-192944(1985), have been employed in the prior art.
A bladder in a bladder type accumulator would deform while it is subjected to a gas pressure and a liquid pressure, and the deformation has such nature that in the initial step of the deformation a bottom portion of the bladder rises in the axial direction, and in the next step of the deformation a deforming portion of the bladder contracts in the radial directions.
However, during this contraction in the radial directions, the deformable portion of the bladder would not always be deformed symmetrically along a circumference. Therefore, in some cases, a deformable portion on one side may approach the outer circumference of the holder earlier than a deformable portion on another side. In the case of the bladder type accumulator associated with the shutter type sensor in the prior art, since the shutter driver is provided only on one side of the deformable portion of the bladder, when the deformable portion of the bladder approaches the outer circumference of the holder uniformly as described above, sometimes the deformable portion of the bladder would not push the shutter driver even if the deformation of the bladder reaches its allowable compression limit.
Moreover, since the bladder would deform in the above-described manner, in the case of the bladder type accumulator associated with the umbrella type sensor in the prior art, the lower limit sensor operates only when the deformable portion of the bladder has deformed in the radial directions, and accordingly, the initial step of deformation of the bladder, that is, the step of the bottom portion of the bladder rising in the axial direction cannot be detected.
Accordingly, it is impossible to finely control the lower limit of the allowable compression range, that is, the maximum available range of the bladder.